In a typical gas turbine engine, a stationary turbine nozzle is disposed at the outlet of a combustor for channeling combustion gases therefrom into a high pressure turbine disposed downstream therefrom. Accordingly, the turbine nozzle is subject to the hot combustion gases and therefore includes suitable cooling arrangements using a portion of compressed air bled from the conventional compressor feeding the combustor. In this environment, the turbine nozzle is subject to differential thermal expansion with adjoining components both radially and axially. This can lead to thermal distortion of the turbine nozzle which must be suitably accommodated for reducing undesirable thermally induced stresses therein and for reducing undesirable leakage of the cooling air which would decrease overall efficiency of the engine.
Accordingly, turbine nozzles are typically segmented around the circumference thereof with each nozzle segment having two or more stationary nozzle vanes therein. Suitable seals are provided between the adjacent nozzle segments, with each of the segments typically being supported by a stationary nozzle support for allowing limited movement or floating thereof to accommodate the differential thermal expansion and contraction between adjacent components. When the engine is operated at suitable power settings, the combustion gases exert an axially aft force against the turbine nozzle segments which rigidly holds the nozzle segments against the nozzle support at the radially inner end of the nozzle as well as holds the radially outer end of the nozzle against a conventional shroud hanger disposed downstream therefrom. However, during assembly and at low power settings of the engine, at idle for example, there is little or no gas load to positively locate the nozzle segments against the nozzle support. Accordingly, suitable means must be provided to hold the nozzle segments in place during assembly and to minimize vibration and wear at low power conditions when the combustion gases do not develop sufficient axial force to firmly hold the nozzle segments in position.
In one conventional configuration, the inner band of a nozzle segment is directly bolted to the nozzle support. This arrangement, however, creates bending stresses in the nozzle and support due to differential thermal expansion and contraction, as well as provides a large area of contact between the nozzle and its support through which heat is conducted from the nozzle vanes into the support increasing the temperature thereof and reducing its useful life. Furthermore, holes required for receiving the bolts inherently create stress concentrations and provide potential leakage paths which must be suitably accommodated in a more complex design. And, the nuts and bolts required to assemble this configuration add undesirable weight to the engine and increase assembly and disassembly time. Boltless support configurations are also conventionally known which use retention pins in tongue-and-groove type configurations between the nozzle inner band and the nozzle support for providing a floating assembly thereof for accommodating differential thermal expansion and contraction. However, these configurations require various seals and are relatively complex.